1. Field of the Invention
This invention relates to methods for producing composite bodies consisting of sintered metal-ceramic particles supported in a metal matrix with the particles surrounded by zones comprising an alloy of the matrix material and dissolved constituents of the particles.
2. Prior Art
My U.S. Pat. No. 4,024,902 discloses a method of forming composite materials consisting of particles of sintered metal-ceramics, in a matrix of steel or like high melting temperature metals. The method involves placing particles of the sintered material in a mold, separately heating the matrix material to above its melting temperature, and then pouring the molten matrixing material into the mold and allowing the mass to naturally cool and solidify. During the period that the molten matrix contacts the sintered particles, the surfaces of the particles are degraded by diffusion and solution of the constituents of the harder material into the matrix. Since the molten metal is at a higher temperature than the original sintering temperature of the particles the portions of the particles at the interface with the hot matrix effectively de-sinter. The quantity and temperature of the molten matrix material and the temperature and geometry of the mold and particles are so chosen that all of the particles will not be totally de-sintered and dissolved into the matrix material before the mass solidifies. The particles will be diminished from their original size but will remain in the finished composite. These particles will be surrounded by zones of a composition of the matrix material, smaller particles and the dissolved constituents of the particles and alloys created by the reaction. In the preferred embodiment of that invention the high temperature material consists of cobalt bound sintered tungsten carbide and the matrixing material a steel alloy. The resultant composite enjoyed a hardness and wear resistance contributed by the tungsten carbide and a toughness contributed by the steel matrix. The diffusion zones surrounding the tungsten carbide particles in the final composite were extremely hard, yet less brittle than the tungsten carbide.
While this process has utility in the formation of a variety of parts, the casting technique imposes certain limitations on the shapes that may be formed. For example, it is extremely difficult to mold in very thin sections without using precision molds and pressure techniques of the type required in an injection molding and it is difficult to form reentrant shapes without using elaborate molds. Also, in some instances the molding process is relatively slow and expensive because of the necessity of forming expendable molds for each part to be formed.
A primary object of the present invention is to provide a method of forming composites having characteristics like those formed by the process of my previous patent, but which avoids the geometric limitations and time and economic restraints of a molding process.